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Exam 2 Key - Name Pg 1 Second Exam BIO 365R Spring 2008...

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Name_______________________________ Pg. 1 Second Exam- BIO 365R- Spring 2008 Write your name on every page . There is a total of 23 questions on 7 pages. Count the pages and be sure you have them all. 1) (6 pts) Describe one complete cycle of excitation- contraction of a skeletal muscle fiber from the time the muscle makes an action potential to the final relaxation of the muscle. The AP travels down the t tubules where it causes the dihydropyridine receptor (DHPS) to activate the ryanodine receptor that is in the wall of the sarcoplasmic reticulum. This causes a release of Ca2+ from the interior of the SR into the sarcoplasm (cytoplasm). The Ca2+ then binds to troponin and this moves tropomyosin away from the myosin-binding site of the actin. Actin and myosin will bind, and an ATP molecule will bind to the myosin head. This causes the myosin head to be released, as ATP is hydrolyzed, the myosin had ratchets back and then bind to actin. As the phosphate is released the myosin head moves forward in a power stroke. Then ADP is released freeing up the binding site for ATP to start the cycle again. Sarcoplasmic Ca2+ is pumped back into the SR by an ATP-powered pump. As Ca2+ comes off the troponin it will be pumped back into the SR. Once Ca2+ is off the troponin, it allows the tropomyosin to move in and cover the myosin binding site and contraction is halted, and relaxation of the muscle can occur. 2) (6 pts) Name three different processes involving Ca 2+ . In each case identify the source of Ca 2+ and name a molecule to which it binds to activate the process. 1) transmitter release, voltage-dependent Ca2+ channels, synaptotagmin 2) moving vesicles up to be docked, VDCC, calmodulin (protein kinase). 3) LTP, NMDA receptor, calmodulin (CAM kinase) 4) skeletal muscle contraction, sarcoplasmic reticulum, troponin 5) smooth muscle contraction, VDCC, calmodulin 6) cardiac muscle contraction, VDCC/sarcoplasmic reticulum, troponin 3) (4 pts) What is the difference between an ionotropic receptor and a metabotropic receptor? Give an example of each one. An ionotropic receptor includes a binding site for the ligand and a channel for the ions to flow through, and example is the nicotinic cholinergic receptor or the AMPA or NMDA receptors or GABA receptors. A metabotropic receptor has a binding site on the receptor and second
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Name_______________________________ Pg. 2 messenger pathway to couple this to the channel. Examples include muscarinic cholinergic receptors, serotonin or beta adrenergic receptors. 4) (5 pts) Below are some events involved in a typical second messenger cascade. Please put these in order by placing a number from 1-5 next to them: ___4__ protein kinase A activated ___2__ G protein activated ___5__ target protein phosphorylated ___1__ neurotransmitter binds to receptor ___3__ adenylate cylase activated 5) (5 pts) Explain how each of the steps in question 4 is terminated.
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